The performances of the three polarization mode dispersion (PMD) emulators commonly used today are analyzed and compared among them through numerical simulation of their differential group delay (DGD) statistical characteristics and PMD vector autocorrelation function. The results demonstrate that to produce DGD that can match theoretical distribution, one DGD generator is adequate, while at least 15 sections are necessary in the emulator built by polarization maintaining fibers and rotatable connectors. And the autocorrelation function of the emulator based on polarization maintaining fibers depends on DGD of every section, while that of the emulator based on DGD generators is smooth and can be regarded as constant outside the central frequency range.